Method for the Production of a Peripherally Closed Hollow Profile Section

ABSTRACT

A method is provided for producing peripherally closed hollow profile section using fluidic internal high pressure. A hollow profile section blank is inserted into a cavity of an internal high pressure forming tool and thereafter being pressed mechanically into an intermediate form approximate to the final form of the hollow profile section, after which, with the tool closed, the intermediate form of the blank is expanded into the final form of the hollow profile section. The blank used in terms of its peripheral length, possesses oversize with respect to the peripheral length of the forming tool cavity. Moreover, the blank material which is excess with respect to the blank material required for the hollow profile section blank to come to bear completely against the cavity of the forming tool is pushed into the blank interior, so as to form an indentation, at the earliest during the pressing operation.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to a method for the production of a peripherally closed hollow profile section.

U.S. Pat. No. 5,070,717 describes a method for producing a peripherally closed hollow profile section, in which a hollow profile section blank, the peripheral length of which corresponds to the peripheral length of a cavity of an internal high pressure forming tool, is inserted into the lower portion of the cavity. The lower portion is formed by a depression of the lower die of the forming tool. Subsequently, the forming tool is closed, the upper die being moved in the direction of the lower die, until they come to bear one against the other and the forming space, delimited by the cavity portions of the upper die and of the lower die, of the forming tool is formed.

Since the height of the hollow profile section blank is considerably greater than the height of the forming space in this conventional method, the hollow profile section blank is acted upon and squeezed by the upper die during the closing movement of the forming tool. As a result of squeezing, the hollow profile section blank assumes a preprofiled intermediate form which is enclosed by the forming space of the forming tool. The intermediate form has corrugations and creases, with the result that the wall of the intermediate form is spaced apart sometimes to a greater and sometimes to a lesser extent from the cavity over the periphery of said intermediate form.

Finally, a fluidic internal high pressure is generated within the intermediate form of the hollow profile section blank in the conventional method, with the result that the intermediate form is expanded into the final form of the hollow profile section. It is often such, however, that the intermediate form of the hollow profile section blank is spaced apart from the cavity to an extent such that the expandability of the hollow profile section blank is not sufficient, during the subsequent expansion by way of fluidic internal high pressure, for the latter to come to bear completely against the cavity of the forming tool and therefore to assume the final form of the hollow profile section. In this case, at these points, cracks can arise which lead to a bursting of the blank during the expansion of the hollow profile section blank by means of internal high pressure. This is particularly so, at points on the blank at which very high internal stresses are formed in the material during the squeezing operation as a result of strain-hardening processes. In order to counteract this unreliability in the forming process, the squeezed hollow profile section blank can, as is known, be formed in a plurality of forming steps by intermediate annealing. This, in turn, is particularly complicated and prolongs the production time of the desired hollow profile section, and therefore, on account of the costs also incurred in this case, there is no suitability for large series production.

An object of the present invention is to provide a method in which the production of a hollow profile section to be preprofiled becomes possible in a relatively simple way and with a high degree of process reliability.

The object has been achieved according to the inventions, by providing a method in which a hollow profile section blank is used, which, in terms of its peripheral length, possesses oversize with respect to the peripheral length of the forming tool cavity, in that the hollow profile section blank is pressed into an intermediate form which, with the blank material which is excess with respect to the blank material required for the hollow profile section blank to come to bear completely against the cavity of the forming tool, overshoots the limit of the forming space reproducing the final form of the hollow profile section, and in that the excess blank material is then pushed into the blank interior, so as to form an indentation, at the earliest during the pressing operation.

The present invention is based on the recognition that as far as possible, the forming space should be completely filled even during the pressing operation, i.e., the preprofiling operation. For this purpose, departing entirely from the prior art, a tubular hollow profile section blank of, for example, circular-cylindrical or oval cross section is used, the peripheral length of which possesses oversize as compared with the peripheral length of the forming tool cavity. As a result, if only because of this, the unformed hollow profile section blank inserted into the tool cavity fills more of the forming space of the forming tool than has hitherto been the case. Consequently, at the same time, more blank material which can be formed in the forming space is also available. As a result of the pressing operation, the overdimensioned hollow profile section blank is pressed even into those regions of the forming space into which a normally dimensioned hollow profile section blank cannot penetrate.

It proves beneficial if, during pressing, the hollow profile section blank can spread out freely into the regions where access is difficult. This may be brought about, on one hand, by a corresponding configuration of the cavity of the forming tool or, on the other hand, by moveable tool parts of the forming tool which with a surface form part of the cavity and are arranged outside the region of spread of the hollow profile section blank during the pressing operation. On account of the overlength or oversize of the hollow profile section blank in the peripheral direction, as compared with the peripheral length of the forming space, the hollow profile section blank, even in the pressed state, has a larger cross section than the forming space.

In order to obtain the desired configuration of the hollow profile section, therefore, the hollow profile section blank must be adapted in terms of its cross section or of its cross-sectional size to the cross section of the forming space. This takes place by the excess hollow profile section blank material being pushed into the blank interior. An indentation is formed in the hollow profile section blank. Expediently, for this purpose, the pushing-in operation takes place at the earliest during the pressing operation. The preprofiled intermediate form of the hollow profile section blank then lies in the forming space such that only low degrees of forming are required in order to bring the hollow profile section blank completely to bear against the forming tool cavity by means of internal high pressure. Cracks which may lead to the bursting of the hollow profile section blank can consequently no longer occur.

The method according to the present invention consequently exhibits a solution, to be implemented relatively simply, as to how a squeezed and thus preprofiled hollow profile section blank can be formed into the final form of the hollow profile section with a high degree of process reliability. In summary, for this purpose, in addition to the normal sequence of the production method, only the pushing-in operation is required, which displaces the excess hollow profile section blank material into the interior of the hollow profile section blank, which, if appropriate, does not even signify a longer production time of the hollow profile section if the pushing-in process takes place during the squeezing operation, i.e., during the preprofiling of the hollow profile section blank.

The provision of an overdimensioned hollow profile section blank does not entail any additional outlay. On the contrary, it is contemplated that, in the production of hollow profile sections of small diameter, the hollow profile section blanks, because of their overdimensioning, can be produced more simply and with a more uniform wall thickness profile, and this can certainly be conducive to the high degree of process reliability of the entire production process of the hollow profile section.

In a currently preferred development of the invention, the pushing-in operation after the formation of the intermediate form takes place by way of a moveable forming element which remains in the push-in position during the internal high pressure forming. On account of the movability of the forming element, in a retracted position of the forming element the hollow profile section blank can spread out freely in the direction of the forming element during the squeezing and pressing operation. Thereby, the hollow profile section blank occupies the forming space of the forming tool virtually completely in this region.

The forming element may be a moveable part of the forming tool, but, for the flexibility of the forming tool in the production of different hollow profile sections, it is advantageous to provide the forming element as a separate component, for example, as an exchangeable slide or ram which can, as required, be removed from the forming tool or be placed into the latter at a suitable point. For this purpose, at the suitable points, removable die segments of the forming tool are to be provided, which, if required, are replaced by the ram or slide. After the pushing-in operation, the forming element remains in its push-in position in a simple way and forms a part of the cavity. By the push-in surface of the forming element being configured specially as a cavity, a complicated moving of the forming element out of the forming tool and subsequent moving-in of a cavity part of the forming tool which replaces the forming element may be dispensed with.

In a further preferred embodiment of the invention, the hollow profile section blank is filled with pressure fluid before the pushing-in operation. By virtue of this measure which affords an internal support for the hollow profile section blank, the occurrence of creases during the pressing operation is counteracted, thus further increasing the degree of process reliability.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.

FIG. 1 is a cross-sectional view of an opening position of a device carrying out the method according to the invention, having an internal high pressure forming tool and a forming element, with a hollow profile section blank inserted into the forming tool,

FIG. 2 is a cross-sectional view of the forming tool from FIG. 1 in the closed position, with a pressed hollow profile section blank, and

FIG. 3 a cross-sectional view of the closed forming tool from FIG. 1, with a hollow profile section blank pushed in by the forming element, after expansion by way of fluidic internal high pressure.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a device 1 for the production of a peripherally closed hollow profile section 2 using fluidic internal high pressure. The device contains an internal high pressure forming tool 5 formed from an upper die 3 and from a lower die 4, and also a forming element 6. Although the forming element 6 may be part of the lower die 4 or of the upper die 3, in the preferred embodiment, however, it is shown as a separate component which is driven mechanically, pneumatically or hydraulically at the rear. The drive 7 causes, the forming element 6 can be moved back and forth with respect to the hollow profile section blank 7. The forming element 6 is displaceable in guides which are arranged on the top side 8 of the lower die 4 and on the underside 9 of the upper die 3.

For the sequence of the production method, according to FIG. 1, a hollow profile section blank 7 is inserted into the cavity 10 of the lower die 4 in the open state of the internal high pressure forming tool 5. Thereafter, the forming tool 5 is closed, the upper die 3 being lowered onto the lower die 4. In this phase, the forming element 6 remains in its retracted non-use position.

In the closed position according to FIG. 2, the forming element 6 is framed by the upper die 3 and the lower die 4. During the closing movement, the upper die 3 acts upon the hitherto still unformed hollow profile section blank 7 and squeezes its form having a circular-cylindrical cross section into an intermediate form 11 which is roughly approximate to the form of the forming space 13, formed by the cavity 10 of the lower die 4 and the cavity 12 of the upper die 3, of the forming tool 5 and, consequently, to the final form of the hollow profile section 2. Since the peripheral length of the hollow profile section blank 7 is markedly greater than the peripheral length of the forming space 13, the intermediate form 11 of the hollow profile section blank 7 projects beyond the forming space 13 and extends toward the forming element 6. The overshot limit 14 of the forming space 13 is illustrated in FIG. 2 by dashes.

After the conclusion of the squeezing and pressing operation, that is to say in the closed position of the forming tool 5, the intermediate form 11 of the hollow profile section blank 7 bears virtually completely against the cavities 10 and 12 of the lower die 4 and of the upper die 3. In the illustrated embodiment, there is only one region 15 of the intermediate form 11 which is spaced apart, but only just, from the cavities 10, 12.

Then, after the forming element 6 has been moved onto the intermediate form 11 of the hollow profile section blank 7, the excess hollow profile section blank material which has overshot the limit 14 of the forming space 13 is pushed in by the forming element, as may be seen from FIG. 3. For this purpose, the forming element 6 has a forming bead 16 which displaces the excess hollow profile section blank material beyond the limit 14 back into the blank interior 17, at the same time forming an indentation 18 on the intermediate form 11.

Above and below the forming bead 16, the surfaces of that side of the forming element 6 which faces the intermediate form 11 are configured so that they form the lateral walls of the forming space 13 and consequently the lateral cavity 19 of the latter. During the pushing-in operation, the intermediate form 11 of the hollow profile section blank 7 may already be filled with pressure fluid, in order to obtain an internal support which is to prevent unwanted creases and collapses during the pushing-in operation. On the other hand, the intermediate form 11 of the hollow profile section blank 7 is then sealed off at each of the two ends by an axial ram and is filled with pressure fluid via axial ducts which run within the axial ram. The axial ram is connected to a fluid high pressure generation system, via which the pressure fluid within the blank interior 7 is pressurized.

While the forming element 6 remains in its push-in position, the intermediate form 11 of the hollow profile section blank 7 expands under the internal high pressure generated and, even in the region 15, comes to bear, true to contour, against the cavities 10 and 12 of the forming tool 5, so as to produce the final form of the hollow profile section 2. Finally, the pressure fluid is depressurized again and the forming element 6 is moved out of its push-in position back into its non-use position. The forming tool 5 is then opened and the ready-formed hollow profile section 2 is extracted from this.

Moreover, the inventive method is to be carried out, and the forming separation of the two dies 3 and 4 is to be provided, such that the generation of the indentation 18 takes place at as favorable a point as possible for the hollow profile section 2 in light of its intended use. In this case, the generated indentation 18, by way of which construction space is saved in the hollow profile section 2, may serve for the free movement and/or for the leadthrough of other assemblies and components and may be used as a receptacle and/or tie-up for other components. Furthermore, the indentation 18 may also be used as a bolster which appreciably increases the rigidity of the hollow profile section 2. If appropriate, the indentation 18, as a decorative fold, may also fulfill special visual requirements. Overall, the method according to the invention produces hollow profile section components with highly complex geometries with a degree of process reliability.

The concept according to the invention may also be adopted in the following scenario. Complex components, in particular frame structure components of motor vehicles, often have cross sections of completely different size over their longitudinal extent according to the installation conditions and the respective local mechanical and/or visual requirements. To produce them from a tubular blank in an internal high pressure forming tool, there is, even after a preprofiling operation, a different degree of forming for each cross section. Conventionally, a hollow profile section blank is selected, the diameter of which corresponds to that of the smallest cross section of the tool cavity adapted exactly to the desired form of the component to be produced. At specific points on the blank, the degrees of forming are such that the expandability of the blank is no longer sufficient to produce the desired form of the component with a high degree of process reliability. Instead, the blank fails by splitting or as a result of bursting phenomena.

To ensure process reliability in the production of the component, then, the selected initial cross section for the hollow profile section blank on the basis of the invention, as compared with the prior art, is in any event larger than the minimum cavity cross section and advantageously corresponds to a cross section which is averaged over the multiplicity of cavity cross sections along the longitudinal extent of the cavity or for the cross sections of the future component to be formed, so that the forming space formed by the cavity is filled to a considerably greater extent. In this case, the blank is squeezed at points of small cross section, in which squeezing would normally impede the operation of closing the forming tool on account of the excess blank material. Owing to the arrangement of the slides and to their retracted position, however, the blank material can be displaced into regions of the forming tool in which the material would otherwise have prevented the closing of the tool. In order to maintain the predetermined external dimensions and not to encroach upon the available construction space of the component, the excess material is pushed back into the interior of the hollow profile section blank by the forming element or forming elements. 

1-3. (canceled)
 4. A method for producing a peripherally closed hollow profile section using fluidic internal high pressure, comprising inserting a hollow profile section blank into a cavity of an internal high pressure forming tool, then pressing the blank mechanically into an intermediate form approximating a final form of the hollow profile section, and thereafter, with the tool in a closed position, expanding the intermediate form of the blank into the final form of the hollow profile section using the internal high pressure, wherein the hollow profile section blank, in terms of a peripheral length thereof, possesses oversize with respect to a peripheral length of the forming tool cavity, and the hollow profile section blank is pressed into the intermediate form which, with the blank material which is excess with respect to the blank material required for the hollow profile section blank to come to bear completely against the cavity of the forming tool, overshoots a limit of the forming space reproducing the final form of the hollow profile section, with the excess blank material then being pushed into the blank interior so as to form an indentation early during the pressing operation.
 5. The method as claimed in claim 4, wherein the pressing-in operation occurs after the formation of the intermediate form by a moveable forming element which remains in the press-in position during the internal high pressure forming.
 6. The method as claimed in claim 4, wherein the hollow profile section blank is filled with pressure fluid before the pressing-in operation.
 7. The method as claimed in claim 5, wherein the pressing-in operation occurs after the formation of the intermediate form by a moveable forming element which remains in the press-in position during the internal high pressure forming. 